Generally, when a call is established in a packet switched telecommunication network such as an IMS network or a Voice over Internet Protocol (VoIP) network or when the call is established from another network such as Circuit Switched network, for example a wireline or mobile telecommunication network, the calling party is connected to the network via a border gateway. When the calling party is subscriber of the packet switched network, then this border gateway constitutes the User to Network Interface (UNI) such as a Proxy Call Session Control Function (P-CSCF) and an access gateway in an IMS network. When the calling party belongs to another (IMS) network, then this border gateway forms a Network to Network Interface (NNI) such as a Media Gateway Control Function (MGCF) plus an IMS Media Gateway (IMS-MGW).
When the call establishment or call release requires an announcement to be generated by a media source and the announcement to be streamed towards the calling party, media will be transferred from a media entity in the user plane (i.e. the plane carrying the media) towards the user equipment of the calling party. For example:                an announcement can be streamed by the media source, for example a Multi Media Resource Function Processor (MRFP), where the MRFP acts under control of a Multimedia Resource Function Controller (MRFC). Media packets can be sent from the MRFP to an IMS access gateway, to an IM-MGW or to a Transition Gateway (TrGW), depending on the calling party, or        a standard voice mail welcome message can be streamed by the voice mail system. Media packets are sent from the Voicemail system to the IMS Access Gateway, the IM-MGW or TrGW, or        contents such as a personalised greeting can be streamed as an announcement from a content system towards the user equipment of the calling party.        
The prerecorded announcements are kept in central storage system(s) in the packet switched telecommunication network and can be distributed to the end-user when required. An example of such an announcement can be an announcement provided to a calling subscriber during call establishment, to inform the calling subscriber that the called party is not reachable.
Each time a call requires an announcement to be streamed to the served party, typically the calling party, it is required that the prerecorded announcement is streamed from the media source specially adapted for generating announcements, within the network to the network border and from the network border to the served party user equipment.
Considering large amounts of calling parties requiring an announcement, vast amounts of prerecorded announcements must be streamed through the packet switched telecommunication network towards these calling parties. At the same time many of such calling parties can require the same announcement. Hence the same media stream is transferred to various media network nodes on the network border with high repetition rate. This frequent streaming of the same data constituting an announcement unnecessarily consumes network capacity and is to be avoided.